1. Field of the Invention
The present invention relates generally to the field of integrated circuit fabrication. More particularly, the present invention relates to temperature measurement of a wafer in a simulated wafer processing environment, such as, for example, on a heating plate in a vacuum chamber. Specifically, a preferred implementation of the present invention relates to a temperature measurement device wherein a plurality of temperature sensors and an associated signal transmitter are attached to a face of the wafer in the form of a set of integrated circuits.
2. Discussion of the Related Art
In the semiconductor industry, many phases of wafer processing, particularly operations involving photoresist, require extraordinary levels of temperature control and uniformity. It is often necessary that the temperature distribution across a 6" wafer be known and controlled to within a fraction of a degree Centigrade. Wafers are fitted with temperature measurement equipment and placed in the processing equipment under simulated wafer processing conditions. Commercially available measurement tools, such as those made by Sensarray Corporation, rely on hard-wired thermocouples, thermistors, or resistive thermal detectors. The resulting device, therefore, is a silicon wafer with a large number of wires affixed to its surface. These wires are brought into a common sheathed lead and a multipin connector, which plugs into an interface module. The entire setup is fragile, because the wires are extremely thin. Conversely, making the wires thicker has an adverse effect on the accuracy because each lead wire acts as a miniature "cold finger" and thus perturbs the very thermal environment that one seeks to measure. Furthermore, the wires interfere with the placement of probes that might be used if one were measuring temperatures in a wafer test bench. Lastly, it is obvious that a hard-wired wafer cannot be used to measure temperatures in a rotating environment such as an operating photoresist spin bowl.
For example, FIG. 1 shows a commercially available wafer temperature measurement metrology product made by Sensarray. The product consists of a "standard" silicon wafer 110 with temperature sensors 120 attached to or embedded in it at various places. The sensors 120 are then attached to sensor leads 130 that are routed through a stress relief clamp 140. The sensor leads 130 continue on to form an unsheathed high compliant lead section 145 and then a sheathed lead section 150. The sensor leads 130 terminate at a connector 160. The connector 160 can carry the signals from the sensors 120 to an external measurement system (not shown).
FIG. 2 shows a commercially available construction for low pressure bake. In this design the leads 130 form a high compliance flat cable vacuum feedthrough 210.
FIG. 3 shows a thermocouple junction 310 conventionally bonded to a silicon wafer 320 with ceramic 330. The thermocouple junction 310 is located in a re-entrant cavity 340 and connected to a pair of thermocouple wires 350.
FIG. 4 shows a thermocouple junction 410 conventionally bonded to a silicon wafer 420 with high temperature epoxy 430. The thermocouple junction 410 is located in a spherical cavity 440 and connected to a pair of thermocouple wires 450.
FIG. 5 shows a resistance temperature detector (RTD) 510 conventionally bonded into a cylindrical cavity 520 of a silicon wafer 530 with high temperature epoxy 540. The RTD 510 includes current source leads 550 and measurement leads 560.
FIG. 6 shows a thermistor 610 conventionally bonded to a silicon wafer 620 with high temperature epoxy 630. The thermistor 610 includes platinum thermistor leads 640 and is located in a tapered thermistor cavity 650. A pair of copper lead wires 660 is located in a tapered lead cavity 670.
All of the designs shown in FIGS. 1-6 include a number of lead wires. All of the designs are fragile and none can be used when the wafer is being rotated.
Therefore, what is needed is a wafer temperature measurement system that is robust, does not interfere with the placement of probes and can be used in a rotating environment. Heretofore, the requirements referred to above have not been fully met.